Serratia marcescens associated with squash leaf chlorosis and necrotic spots in Iran

In autumn 2011, a survey was conducted for the identification of plant pathogenic bacteria affecting Cucurbitaceae grown in southwestern Iran. Squash ( Cucurbita pepo var. styriaca ) plants with suspected bacterial symptoms, i.e. necrotic spots surrounded by chlorotic haloes, were collected and brought to the laboratory for further analysis. Two Gram-negative, red-pigmented bacterial strains were isolated from squash leaves in Shushtar county, Khuzestan province. The isolates induced hypersensitive reaction (HR) on tobacco plants 24 h post-inoculation. A pathogenicity test on 25-day-old squash plants yielded symptoms consisting of necrotic spots surrounded by chlorotic haloes that appeared 5–10 days post-inoculation. The causal agent was identified as Serratia marcescens based on biochemical and phylogenetic analyses. Phylogenetic analysis of 16S rRNA, gyrB and groE genes sequences showed that the isolates have 99–100% similarity with S. marcescens strains previously described as pathogenic to bell pepper and corn plants. Although non-pigmented strains of S. marcescens have previously been described as the causal agents of cucurbit yellow vine disease, this is the first report of a HR-inducing red-pigmented strain of the bacterium associated with squash leaf chlorosis and necrosis.